1. Field of the Invention
This invention relates to belt-type stepless speed shifting transmission systems, as used on vehicles such as automobiles, motorcycles, and the like, and, more particularly, to a system wherein belt thrust force is automatically varied in response to vehicle speed and output load.
2. Background Art
Belt-type stepless speed shifting transmissions for motorcycles, automobiles, and the like, are known in the art. Generally, these systems employ parallel input and output shafts, each of which carries a belt-operated sheave consisting of a stationary pulley piece and a cooperating movable pulley piece. The movable and stationary pulley pieces have confronting belt-engaging surfaces cooperatively defining a V-shaped groove for the reception of a V-belt which is trained about the input and output sheaves. Varying the axial "thrust force" on the belt, by shifting the movable pulley parts relative to the cooperating stationary pulley parts, varies the effective sheave diameters and, as an incident thereof, the speed ratios of the input and output shafts varies. In conventional systems, the thrust force on the belt is generally developed through hydraulic pressure or a spring force acting on the pulley piece pairs.
Often, these prior art structures are quite complicated. For example, U.S. Pat. No. 4,601,680 shows a system wherein hydraulic pressure is developed on the side of a movable pulley piece, with the amount of pressure dictated by an electronic controller. A large quantity of data needs to be inputted into the controller and such systems generally require a significant number of sensors. The overall system may be quite complicated and expensive as the number and sophistication of components increase. With complexity, the potential for failure also increases.
Another drawback with prior art systems of the type utilizing biasing springs, and the like, is that these systems are commonly not sensitive to minor variations in vehicle speed and load. Further, such systems generally react poorly to abrupt acceleration.